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BMS Processing Class

A Course23.com Production

"Stop, Pause, and Think..." -- Ms. Elwell
"Take your time, it isn't a race" -- Mr. Helmke

  • Home
  • Conditionals and Logic
    • Conditionals 1: Boolean Expressions and the If Statement
      • Activity 16 (IF1)
    • Conditionals 2: If/Else Statements
      • Activity 17 (IFELSE1)
    • Conditionals 3: Else If Statements
      • Activity 18 (elseif1)
      • Activity 19
      • Activity 20 (elseif3)
      • Activity 21
    • Logical Operators
      • Activity 22 (And1)
      • Activity 23
      • Activity 24 (SingleRollover)
      • Activity 25 (FourSquareRollover)
      • Activity 26 (MoveWhenPressed)
      • Activity 27 (bouncy ball 1)
      • Activity 28 (bouncy ball 2)
  • Functions
    • Moving Shapes 1
      • Activity 29 (StarBright)
      • Activity 30 (CreatureAtOrigin)
    • Moving Shapes 2
      • Activity 31 (drawCreatureFunction)
      • Activity 32 (BouncingCreatures)
    • Rotating Shapes
      • Activity 33 (RotatingCreatures)
      • Activity 34 (RotatingShapes)
      • Activity 35 (RotatingShapes2)
  • Looping and Arrays
    • Loops 1
      • Activity 36 (ShapeLoop)
      • Activity 37 (RandomLoop1)
    • Loops 2
      • Activity 38 (Deg2Rad)
      • Activity 39 (NumberLoop1)
      • Activity 40 (NumberLoop2)
    • Arrays 1
      • Activity 41
      • Activity 42
      • Activity 43
    • Arrays 2
      • Activity 44
      • Activity 45
      • Activity 46
  • Final Topics
    • Introduction
    • Particle Systems
    • Maze Game
  • Resources

Conditionals 1: Boolean Expressions and the If Statement

Boolean Expressions

A Boolean expression (named for the mathematician George Boole) is an expression that can be either true or false.

For example:

  • My favorite color is blue == true
  • I am afraid of the dark == false
  • Coding is fun after all == true

In the logic of computers, we test relationships between numbers:

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  15 is greater than 20 == false
  5 equals 5 == true
  32 is less than or equal to 33 == true

let’s think of this in terms of code and variables:

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  x > 20 – depends on the current value of x
  y == 5 – depends on the current value of y
  z <= 33 – depends on the current value of z

The following are standard boolean operations in Processing:

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  >    greater than
  <    less than
  >=   greater than or equal to
  <=   less than or equal to
  ==   equal to
  !=   not equal to

“If” Statements

Conditionals operate within the sketch as questions. Is 30 greater than 10? If the answer is yes (i.e., true), you can choose to execute certain instructions (such as draw a rectangle); if the answer is no (i.e., false), those instructions are ignored. This introduces the idea of branching; depending on various conditions, the program can follow different paths.

With the question, if the mouse is on the left side of the screen, draw a rectangle on the left side of the screen, you would code it as follows:

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function setup() {
  createCanvas(windowWidth, windowHeight);
}
 
function draw() {
  background(0);
  if (mouseX < windowWidth/2) {
 
    fill(255);
    rect(0, 0, windowWidth/2, windowHeight);
  }
}

In the above code, remember that mouseX is a system variable that always holds the current X coordinate of the mouse. windowWidth/2 is the X coordinate of 1/2 of the screen. Together, mouseX < windowWidth/2 is true when the X position of the mouse is on the left half of the screen.

Complete Activity 16

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Required Reading:

Course Coding Standards

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